Methods and apparatuses for isomerization of paraffins

ABSTRACT

Embodiments of methods and apparatuses for isomerization of paraffins are provided. In one example, a method comprises the steps of compressing a C 4   −  hydrocarbons-containing stabilizer vapor stream to form a compressed C 4   −  hydrocarbons-containing stabilizer stream. A C 4  hydrocarbons-containing feed stream that comprises unbranched C 4  hydrocarbons is contacted with a chloride-promoted isomerization catalyst in the presence of hydrogen to form a branched C 4 hydrocarbons-containing reaction zone effluent. At least a portion of the compressed C 4   −  hydrocarbons-containing stabilizer stream is combined with the branched C 4  hydrocarbons-containing reaction zone effluent to form a C 4  hydrocarbons-containing combined stream. The C 4  hydrocarbons-containing combined stream is separated into a C 3   −  hydrocarbons-containing stabilizer vapor stream and a C 4  hydrocarbons-rich product stream that comprises branched C 4  hydrocarbons.

TECHNICAL FIELD

The technical field relates generally to methods and apparatuses forisomerization of hydrocarbons, and more particularly relates to methodsand apparatuses for isomerization of paraffins with recovery of C₄hydrocarbons.

BACKGROUND

Isomerization processes are widely used by many refiners to rearrangethe molecular structure of straight chain paraffinic hydrocarbons tomore highly branched hydrocarbons. Generally, these more highly branchedhydrocarbons have relatively high octane ratings.

Paraffin feeds for C₅/C₆ hydrocarbons isomerization processes cancontain cyclic C₆ ⁺ hydrocarbons such as benzene and cyclic C₇ ⁺hydrocarbons. As used herein, C_(x) hydrocarbons means hydrocarbonmolecules that have “X” number of carbon atoms, C_(x) ⁺ hydrocarbonsmeans hydrocarbon molecules that have “X” and more than “X” number ofcarbon atoms, and C_(x) ⁻ hydrocarbons means hydrocarbon molecules thathave “X” and less than “X” number of carbon atoms. As used herein, C₅/C₆hydrocarbons mean C₅ hydrocarbons and/or C₆ hydrocarbons. When theweight percent of cyclic C₆ ⁺ hydrocarbons in the paraffin feed is about20% or greater (also referred to as an X-factor of 20 or greater inwhich the X-factor is defined as the sum of the weight percent of thecyclic C₆ hydrocarbons plus C₇ ⁺ hydrocarbons in the feed, e.g.,benzene+cyclohexane+methylcyclopentane+C₇ ⁺), the paraffin feed isconsidered a “hard feed to isomerize.” In particular, the C₇ ⁺hydrocarbons and to a much lesser extent C₅ and C₆ hydrocarbons in thereactor tend to hydrocrack, producing C₄ hydrocarbons as well as otherlighter hydrocarbons, e.g., C₃ ⁺ hydrocarbons. The C₄ hydrocarbons havesignificant caloric and economic value. Unfortunately, the C₄hydrocarbons are traditionally removed in an off-gas stream of C₅/C₆hydrocarbons isomerization processes and burned because the investmentand operating costs for recovering the C₄ hydrocarbons are prohibitivelyexpensive.

Accordingly, it is desirable to provide methods and apparatuses forisomerization of paraffins including recovery of C₄ hydrocarbons withreduced overall investment and/or operating costs. Moreover, it isdesirable to provide methods and apparatuses for isomerization ofparaffins including recovery of C₄ hydrocarbons, such as for C₅/C₆hydrocarbons isomerization processes that have paraffinic feed streamsthat may contain some C₇ ⁺ hydrocarbons. Furthermore, other desirablefeatures and characteristics of the present invention will becomeapparent from the subsequent detailed description and the appendedclaims, taken in conjunction with the accompanying drawings and thisbackground.

BRIEF SUMMARY

Methods and apparatuses for isomerization of paraffins are providedherein. In accordance with an exemplary embodiment, a method forisomerization of paraffins comprises the steps of compressing a C₄ ⁻hydrocarbons-containing stabilizer vapor stream to form a compressed C₄⁻ hydrocarbons-containing stabilizer stream. A C₄hydrocarbons-containing feed stream that comprises unbranched C₄hydrocarbons is contacted with a chloride-promoted isomerizationcatalyst in the presence of hydrogen to form a branched C₄hydrocarbons-containing reaction zone effluent. At least a portion ofthe compressed C₄ ⁻ hydrocarbons-containing stabilizer stream iscombined with the branched C₄ hydrocarbons-containing reaction zoneeffluent to form a C₄ hydrocarbons-containing combined stream. The C₄hydrocarbons-containing combined stream is separated into a C₃ ⁻hydrocarbons-containing stabilizer vapor stream and a C₄hydrocarbons-rich product stream that comprises branched C₄hydrocarbons.

In accordance with another exemplary embodiment, a method forisomerization of paraffins is provided. The method comprises the stepsof contacting a C₅ ⁺ hydrocarbons-containing feed stream that comprisesunbranched C₅/C₆ hydrocarbons with a chloride-promoted isomerizationcatalyst in the presence of hydrogen to form a branched C₅ ⁺hydrocarbons-containing reaction zone effluent. The branched C₅ ⁺hydrocarbons-containing reaction zone effluent is separated into a C₄ ⁻hydrocarbons-containing stabilizer vapor stream and a C₅ ⁺hydrocarbon-rich product stream that comprises branched C₅ ⁺hydrocarbons. The C₄ ⁻ hydrocarbons-containing stabilizer vapor streamis compressed to form a compressed C₄ ⁻ hydrocarbons-containingstabilizer stream. The compressed C₄ ⁻ hydrocarbons-containingstabilizer stream is cooled to form a cooled, compressed C₄ ⁻hydrocarbons-containing stabilizer stream. The cooled, compressed C₄ ⁻hydrocarbons-containing stabilizer stream is separated into a C₄hydrocarbons-containing liquid stream and a C₃ ⁻ hydrocarbons-containingoff gas stream. The C₄ hydrocarbons-containing liquid stream is combinedwith a branched C₄ hydrocarbons-containing reaction zone effluent toform a C₄ hydrocarbons-containing combined stream. The C₄hydrocarbons-containing combined stream is separated into a C₃ ⁻hydrocarbons-containing stabilizer vapor stream and a C₄hydrocarbons-rich product stream that comprises branched C₄hydrocarbons.

In accordance with another exemplary embodiment, an apparatus forisomerization of paraffins is provided. The apparatus comprises acompressor that is configured to receive and compress a C₄ ⁻hydrocarbons-containing stabilizer vapor stream to form a compressed C₄⁻ hydrocarbons-containing stabilizer stream. A reaction zone contains achloride-promoted isomerization catalyst in the presence of hydrogen.The reaction zone is configured to receive a C₄ hydrocarbons-containingfeed stream that comprises unbranched C₄ hydrocarbons and to operate atisomerization conditions effective to form a branched C₄hydrocarbons-containing reaction zone effluent. The apparatus isconfigured to combine at least a portion of the compressed C₄ ⁻hydrocarbons-containing stabilizer stream and the branched C₄hydrocarbons-containing reaction zone effluent to form a C₄hydrocarbons-containing combined stream. A stabilizer zone is configuredto receive and separate the C₄ hydrocarbons-containing combined streaminto a C₃ ⁻ hydrocarbons-containing stabilizer vapor stream and a C₄hydrocarbons-rich product stream that comprises branched C₄hydrocarbons.

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments will hereinafter be described in conjunctionwith the following drawing figures, wherein like numerals denote likeelements, and wherein:

FIG. 1 schematically illustrates an apparatus and method forisomerization of paraffins in accordance with an exemplary embodiment;and

FIG. 2 schematically illustrates an apparatus and method forisomerization of paraffins in accordance with another exemplaryembodiment.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and isnot intended to limit the various embodiments or the application anduses thereof. Furthermore, there is no intention to be bound by anytheory presented in the preceding background or the following detaileddescription.

Various embodiments contemplated herein relate to methods andapparatuses for isomerization of paraffins. Unlike the prior art, theexemplary embodiments of the apparatus taught herein integrate a C₅/C₆hydrocarbons isomerization section with a C₄ hydrocarbons isomerizationsection. In the C₅/C₆ hydrocarbons isomerization section, a C₅ ⁺hydrocarbons-containing feed stream that comprises unbranched C₅/C₆hydrocarbons is contacted with a chloride-promoted isomerizationcatalyst in the presence of hydrogen in a first reaction zone to form abranched C₅ ⁺ hydrocarbons-containing reaction zone effluent. As usedherein, the term “zone” refers to an area including one or moreequipment items and/or one or more sub-zones. Equipment items caninclude one or more reactors or reactor vessels, heaters, exchangers,dryers, pipes, pumps, compressors, and controllers. Additionally, anequipment item, such as a reactor, dryer, or vessel, can further includeone or more zones or sub-zones.

In an exemplary embodiment, the branched C₅ ⁺ hydrocarbons-containingreaction zone effluent is introduced to a first stabilizer zone andseparated into a C₄ hydrocarbons-containing stabilizer vapor stream anda C₅ ⁺ hydrocarbon-rich product stream that comprises branched C₅ ⁺hydrocarbons. The C₄ ⁻ hydrocarbons-containing stabilizer vapor streamcomprises C₄ hydrocarbons, C₃ ⁻ hydrocarbons, hydrogen, and HCl. The C₄⁻ hydrocarbons-containing stabilizer vapor stream is compressed to forma compressed C₄ ⁻ hydrocarbons-containing stabilizer stream.

In the C₄ hydrocarbons isomerization section, a C₄hydrocarbons-containing feed stream that comprises unbranched C₄hydrocarbons is contacted with a chloride-promoted isomerizationcatalyst in the presence of hydrogen in a second reaction zone to form abranched C₄ hydrocarbons-containing reaction zone effluent. In anexemplary embodiment, at least a portion of the compressed C₄ ⁻hydrocarbons-containing stabilizer stream from the C₅/C₆ hydrocarbonsisomerization section is introduced to and combined with the branched C₄hydrocarbons-containing reaction zone effluent to form a C₄hydrocarbons-containing combined stream. The C₄ hydrocarbons-containingcombined stream is separated in a second stabilizer into a C₃ ⁻hydrocarbons-containing stabilizer vapor stream and a C₄hydrocarbons-rich product stream. In an exemplary embodiment, the C₄hydrocarbons-rich product stream contains both branched and unbranchedC₄ hydrocarbons correspondingly from the C₄ hydrocarbons isomerizationsection and the C₅/C₆ hydrocarbons isomerization section. The C₃ ⁻hydrocarbons-containing stabilizer vapor stream comprises C₃hydrocarbons, hydrogen, and HCl. In an exemplary embodiment, the C₃ ⁻hydrocarbons-containing stabilizer vapor stream is introduced to ascrubbing zone and is scrubbed with a caustic to neutralize HCl. Theneutralized C₃ ⁻ hydrocarbons-containing stabilizer vapor stream isremoved and may be burned as fuel gas.

Currently, some refiners employ separate isomerization processes fortheir operations, one for C₅/C₆ hydrocarbons isomerization and anotherfor C₄ hydrocarbons isomerization. These isomerization processes oftenutilize correspondingly similar but independent equipment items, such asequipment for the scrubbing zones, which can have significant investmentand operational cost. By integrating the C₅/C₆ hydrocarbonsisomerization section with the C₄ hydrocarbons isomerization section inaccordance with the various embodiments described herein, the C₄hydrocarbons in the C₄ ⁻ hydrocarbons-containing stabilizer vapor streamfrom the C₅/C₆ hydrocarbons isomerization section can be recovered inthe C₄ hydrocarbons isomerization section. Additionally, in an exemplaryembodiment, the single scrubbing zone in the C₄ hydrocarbonsisomerization section can be used to neutralize HCl from both the C₅/C₆hydrocarbons isomerization section and the C₄ hydrocarbons isomerizationsection, thereby eliminating a separate scrubbing zone for the C₅/C₆hydrocarbons isomerization process. As such, the total investment andoperating costs for the isomerization process can be reduced compared tothe total investment and operating costs for two separate isomerizationprocesses, one for C₅/C₆ hydrocarbons isomerization and another for C₄hydrocarbons isomerization.

Referring to FIG. 1, a schematic depiction of an apparatus 10 forisomerization of paraffins in accordance with an exemplary embodiment isprovided. The apparatus 10 is utilized for a paraffin isomerizationprocess that converts normal paraffins to branched paraffins. Asillustrated, the apparatus 10 comprises a C₅/C₆ hydrocarbonsisomerization section 12 and a C₄ hydrocarbons isomerization section 14that is in fluid communication with the C₅/C₆ hydrocarbons isomerizationsection 12.

In an exemplary embodiment, the C₅/C₆ hydrocarbons isomerization section12 comprises a reaction zone 16, a stabilizer zone 18, a compressionsuction drum 20, a compressor 22, a cooler 24, and a separator 26 thatare in fluid communication. The C₄ hydrocarbons isomerization section 14comprises a reaction zone 28, a stabilizer zone 30, and a scrubbing zone32 that are in fluid communication.

A C₅ ⁺ hydrocarbons-containing feed stream 33 is introduced to the C₅/C₆hydrocarbons isomerization section 12. The C₅ ⁺ hydrocarbons-containingfeed stream 33 comprises normal or unbranched paraffinic C₅/C₆hydrocarbons, such as normal pentane and normal hexane. In an exemplaryembodiment, the C₅ ⁺ hydrocarbons-containing feed stream 33 isrelatively rich in C₅/C₆ hydrocarbons and further comprises cyclic C₆ ⁺and C₇ ⁺ hydrocarbons. In one example, the C₅ ⁺ hydrocarbons-containingfeed stream 33 comprises the cyclic C₆ ⁺and C₇ ⁺ hydrocarbons in anamount of about 10 weight percent (wt. %) or greater, such as from about10 to about 50 wt. % or greater, for example from about 20 to about 30wt. %, of the C₅ ⁺ hydrocarbons-containing feed stream 33. As such, theC₅ ⁺ hydrocarbons-containing feed stream 33 is considered a feed streamthat is “hard to isomerize,” which can result in some hydrocracking ofthe cyclic C₆ ⁺ and C₇ ⁺ hydrocarbons during the isomerization of theC₅/C₆ hydrocarbons, thereby producing C₄ ⁻ hydrocarbons.

A hydrogen-containing gas feed 34 and a chloride promoter stream 36(e.g., containing perchloroethylene or the like) are introduced to theC₅ ⁺ hydrocarbons-containing feed stream 33 to form a combined stream38. Although not illustrated, the C₅ ⁺ hydrocarbons-containing feedstream 33, the hydrogen-containing gas feed 34, the chloride promoterstream 36, and/or the combined stream 38 may be passed through adryer(s), a heat exchanger(s), and/or a heater(s) so that the combinedstream 38 is dry and heated while advancing through the reaction zone16. In an exemplary embodiment, the combined stream 38 is at atemperature of about 90 to about 210° C. in the reaction zone 16.

In an exemplary embodiment, the reaction zone 16 comprises a fixed-bedcatalytic reactor operating at a temperature of from about 90 to about210° C. and contains an isomerization catalyst that is activated by HClby the decomposition of chloride promoter from the chloride promoterstream 36 to form a high-activity chloride-promoted isomerizationcatalyst. Non-limiting examples of the isomerization catalyst includealumina catalyst, platinum aluminum catalyst, and the like that can bechlorinated. The chloride-promoted isomerization catalyst in thepresence of hydrogen is effective to isomerize the normal paraffins tobranched paraffins (e.g., branched pentane and/or branched hexane) toproduce a branched C₅ ⁺ hydrocarbons-containing reaction zone effluent40. The branched C₅ ⁺ hydrocarbons-containing reaction zone effluent 40contains branched and some unbranched C₅/C₆ hydrocarbons, C₄hydrocarbons, C₃ hydrocarbons, some naphthenes and C₇ paraffins,hydrogen (e.g., unreacted hydrogen), HCl, and possibly otherchloride-containing compounds.

The branched C₅ ⁺ hydrocarbons-containing reaction zone effluent 40 ispassed along to the stabilizer zone 18 and is separated at separationconditions into a C₄ ⁺ hydrocarbons-containing stabilizer vapor stream42 and a C₅ ⁺ hydrocarbon-rich product stream 44. In an exemplaryembodiment, the stabilizer zone 18 (e.g., stabilizer overhead receiver)is operating at a temperature of from about 30 to about 45° C. and apressure of from about 1030 to about 1720 kPa gauge. In an exemplaryembodiment, the C₄ ⁻ hydrocarbons-containing stabilizer vapor stream 42comprises C₄ hydrocarbons, C₃ ⁻ hydrocarbons, hydrogen, and HCl. The C₅⁺ hydrocarbon-rich product stream 44 is rich in branched C₅ ⁺hydrocarbons (e.g., C₅/C₆ hydrocarbons), such as branched pentanesand/or branched hexanes, and is removed from the apparatus 10 asproduct.

As illustrated, the C₄ ⁻ hydrocarbons-containing stabilizer vapor stream42 is passed through the compression suction drum 20 to remove mistdroplets and/or deposits from the vapor stream 42 and to form ademisted, C₄ ⁻ hydrocarbons-containing stabilizer vapor stream 46. In anexemplary embodiment, the demisted, C₄ ⁻ hydrocarbons-containingstabilizer vapor stream 46 is introduced to the compressor 22 at atemperature of from about 30 to about 45° C. and a pressure of fromabout 1030 to about 1720 kPa gauge. The compressor 22 compresses thedemisted, C₄ ⁻ hydrocarbons-containing stabilizer vapor stream 46 toform a compressed C₄ ⁻ hydrocarbons-containing stabilizer stream 48. Inan exemplary embodiment, the compressor 22 pressurizes the vapor stream46 to forms the compressed C₄ ⁻ hydrocarbons-containing stabilizerstream 48 having a pressure of from about 2760 to about 4210 kPa gaugeand a temperature of from about 70 to about 120° C.

As illustrated, the compressed C₄ ⁻ hydrocarbons-containing stabilizerstream 48 is passed along to the cooler 24, which cools the compressedC₄ ⁻ hydrocarbons-containing stabilizer stream 48 to form a cooled,compressed C₄ ⁻ hydrocarbons-containing stabilizer stream 50. In anexemplary embodiment, the cooled, compressed C₄ ⁻hydrocarbons-containing stabilizer stream 50 has a temperature of fromabout 0 to about 45° C., such as from about 30 to about 45° C., and apressure of from about 2660 to about 4140 kPa gauge. The cooled,compressed C₄ ⁻ hydrocarbons-containing stabilizer stream 50 isseparated in the separator 26 to form a C₄ hydrocarbons-containingliquid stream 52 and a C₃ ⁻ hydrocarbons-containing off gas stream 54.In an exemplary embodiment, the C₄ hydrocarbons-containing liquid stream52 is rich in C₄ hydrocarbons, e.g., branched and/or unbranchedparaffinic C₄ hydrocarbons, a significant portion of which were formedin the reaction zone 16 due to hydrocracking of C₇ ⁺ hydrocarbonscontained in the C₅ ⁺ hydrocarbons-containing feed stream 33. The C₃ ⁻hydrocarbons-containing off gas stream 54 comprises C₃ ⁻ hydrocarbons,hydrogen, and HCl.

The C₃ ⁻ hydrocarbons-containing off gas stream 54 may be divided intoportions 55 and 57. In an exemplary embodiment, at least the portion 55of the C₃ ⁻ hydrocarbons-containing off gas stream 54 is recycled backto the C₅ ⁺ hydrocarbons-containing feed stream 33, e.g., via directintroduction to stream 33, 34, or 38, for introduction to the reactionzone 16. As illustrated, the portion 55 of the C₃ ⁻hydrocarbons-containing off gas stream 54 is introduced to thehydrogen-containing gas feed 34, which is introduced to the C₅ ⁺hydrocarbons-containing feed stream 33 to form the combined stream 38.As such, HCl and hydrogen contained in the portion 55 of the C₃ ⁻hydrocarbons-containing off gas stream 54 helped to replenish hydrogenand chloride promoter consumed during the isomerization reaction,thereby reducing the amount of makeup hydrogen and chloride promoterneeded from the hydrogen-containing gas feed 34 and the chloridepromoter stream 36, respectively. In an exemplary embodiment, at leastthe portion 57 of the C₃ ⁻ hydrocarbons-containing off gas stream 54 ispassed along to the C₄ hydrocarbons isomerization section 14 for furtherprocessing and to neutralize HCl in the off gas stream 54 as discussedin further detail below. In an exemplary embodiment and as illustrated,at least a portion 57′ of the portion 57 of the C₃ ⁻hydrocarbons-containing off gas stream 54 is introduced to the stream 58and/or 62 to help replenish hydrogen and chloride promoter consumedduring the isomerization reaction, thereby reducing the amount of makeuphydrogen and/or chloride promoter needed from the hydrogen-containinggas feed 58 and/or the chloride promoter stream 60, respectively. In anexemplary embodiment, C₃ ⁻ hydrocarbons-containing off gas stream 54 isdivided such that portion 55 corresponds to about 30 to about 70%, suchas from about 40 to about 60%, of the mass flow rate of the C₃ ⁻hydrocarbons-containing off gas stream 54 and the portion 57 correspondsto about 30 to about 70%, such as from about 40 to about 60%, of themass flow rate of the off gas stream 54. In this embodiment, the ratioof the portion 55 to the portion 57 is such that the C₅/C₆ hydrocarbonsisomerization section 12 maintains a suitable material balance that isnot overly weighted with light end hydrocarbons, e.g., C₃ ⁻hydrocarbons.

The C₄ hydrocarbons-containing liquid stream 52 is passed along to theC₄ hydrocarbons isomerization section 14 downstream from the reactionzone 28. Upstream from the reaction zone 28, a C₄hydrocarbons-containing feed stream 56 is introduced to the C₄hydrocarbons isomerization section 14. The C₄ hydrocarbons-containingfeed stream 56 comprises normal or unbranched paraffinic C₄hydrocarbons, such as normal butane. A hydrogen-containing gas feed 58and a chloride promoter stream 60 (e.g., containing perchloroethylene orthe like) are introduced to the C₄ hydrocarbons-containing feed stream56 to form a combined stream 62. Although not illustrated, the C₄hydrocarbons-containing feed stream 56, the hydrogen-containing gasstream 58, the chloride promoter stream 60, and/or the combined stream62 may be passed through a dryer(s), a heat exchanger(s), and/or aheater(s) so that the combined stream 62 is dry and heated whileadvancing through the reaction zone 28. In an exemplary embodiment, thecombined stream 38 is at a temperature of about 90 to about 210° C. inthe reaction zone 16.

In an exemplary embodiment, the reaction zone 28 comprises a fixed-bedcatalytic reactor operating at a temperature of from about 90 to about210° C. and contains an isomerization catalyst that is activated by HClby the decomposition of chloride promoter from the chloride promoterstream 60 to form a high-activity chloride-promoted isomerizationcatalyst as described above in relation to the reaction zone 16. Thechloride-promoted isomerization catalyst in the presence of hydrogen iseffective to isomerize the normal paraffins to branched paraffins (e.g.,branched butane) to produce a branched C₄ hydrocarbons-containingreaction zone effluent 64. The branched C₄ hydrocarbons-containingreaction zone effluent 64 contains branched and unbranched C₄hydrocarbons, C₃ ⁻ hydrocarbons, hydrogen (e.g., unreacted hydrogen),HCl, and possibly other chloride-containing compounds and otherhydrocarbons such as C₅ hydrocarbons and some trace C₆ ⁺ hydrocarbons.

In an exemplary embodiment, the C₄ hydrocarbons-containing liquid stream52 is combined with the branched C₄ hydrocarbons-containing reactionzone effluent 64 to form a C₄ hydrocarbons-containing combined stream66. In an exemplary embodiment, the C₄ hydrocarbons-containing combinedstream 66 has a pressure of from about 2000 to about 2760 kPa gauge anda temperature of from about 30 to about 150° C., such as from about 80to about 110° C. The C₄ hydrocarbons-containing combined stream 66 ispassed through the stabilizer zone 30 and separated into a C₃ ⁻hydrocarbons-containing stabilizer vapor stream 68 and a C₄hydrocarbons-rich product stream 70. The C₄ hydrocarbons-rich productstream 70 is rich in C₄ hydrocarbons including branched C₄ hydrocarbons,such as branched butane or isobutane, and is removed from the apparatus10 as product. The C₃ ⁻ hydrocarbons-containing stabilizer vapor stream68 comprises C₃ ⁻ hydrocarbons, hydrogen, and HCl. In an exemplaryembodiment, the C₃ hydrocarbons-containing stabilizer vapor stream 68has a pressure of from about 1000 to about 2410 kPa gauge, such as fromabout 1720 to about 2410 kPa gauge, and a temperature of from about 0(or lower, e.g., −40° C.) to about 45° C.

In an exemplary embodiment, at least the portion 57 of the C₃ ⁻hydrocarbons-containing off gas stream 54 is combined with the C₃ ⁻hydrocarbons-containing stabilizer vapor stream 68 to form a C₃ ⁻hydrocarbons-containing combined stream 72. The C₃ ⁻hydrocarbons-containing combined stream 72 comprises C₃ ⁻ hydrocarbons,hydrogen, and HCl. The C₃ ⁻ hydrocarbons-containing combined stream 72is passed to the scrubbing zone 32. The scrubbing zone 32 scrubs the C₃⁻ hydrocarbons-containing combined stream 72 by neutralizing the HClcontained therein with a caustic 74, e.g., sodium hydroxide, to form aneutralized off gas stream 76 that is removed from the apparatus 10 andmay be burned as fuel gas, for example.

Referring to FIG. 2, the apparatus 10 in accordance with anotherexemplary embodiment is provided. The apparatus 10 as shown in FIG. 2 issimilarly configured to the apparatus 10 as shown in FIG. 1 anddiscussed above but without the cooler 24, the separator 26, and theresulting streams 50, 52, 54, 55, and 57. In this embodiment, thecompressed C₄ ⁻ hydrocarbons-containing stabilizer stream 48 from theC₅/C₆ hydrocarbons isomerization section 12 is passed along to the C₄hydrocarbons isomerization section 14 and combined with the branched C₄hydrocarbons-containing reaction zone effluent 64 to form the C₄hydrocarbons-containing combined stream 66. In an exemplary embodiment,the C₄ hydrocarbons-containing combined stream 66 has a pressure of fromabout 2000 to about 2760 kPa gauge and a temperature of from about 30 toabout 150° C.

As discussed above, the C₄ hydrocarbons-containing combined stream 66 isseparated in the stabilizer zone 30 into the C₃ ⁻hydrocarbons-containing stabilizer vapor stream 68 and the C₄hydrocarbons-rich product stream 70. The C₄ hydrocarbons-rich productstream 70 is rich in C₄ hydrocarbons including branched C₄ hydrocarbons,such as branched butane or isobutane, and is removed from the apparatus10 as product. The C₃ ⁻ hydrocarbons-containing stabilizer vapor stream68 comprises C₃ ⁻ hydrocarbons, hydrogen, and HCl. In an exemplaryembodiment, the C₃ ⁻ hydrocarbons-containing stabilizer vapor stream 68has a pressure of from about 1000 to about 2410 kPa gauge, such as fromabout 1720 to about 2410 kPa gauge, and a temperature of from about 0(or lower, e.g., −40° C.) to about 45° C.

In an exemplary embodiment, the C₃ ⁻ hydrocarbons-containing stabilizervapor stream 68 is passed to the scrubbing zone 32. The scrubbing zone32 scrubs the C₃ ⁻ hydrocarbons-containing stabilizer vapor stream 68 byneutralizing the HCl contained therein with the caustic 74 to form theneutralized off gas stream 76 that is removed from the apparatus 10 andmay be burned as fuel gas, for example.

Accordingly, methods and apparatuses for isomerization of paraffins havebeen described. The exemplary embodiments taught herein integrate aC₅/C₆ hydrocarbons isomerization section with a C₄ hydrocarbonsisomerization section. By integrating the C₅/C₆ hydrocarbonsisomerization section with the C₄ hydrocarbons isomerization section asdescribed herein, C₄ hydrocarbons contained in a stabilizer vapor streamfrom the C₅/C₆ hydrocarbons isomerization section that would otherwisebe burned as fuel gas can be recovered in the C₄ hydrocarbonsisomerization section as part of a product stream.

While at least one exemplary embodiment has been presented in theforegoing detailed description of the disclosure, it should beappreciated that a vast number of variations exist. It should also beappreciated that the exemplary embodiment or exemplary embodiments areonly examples, and are not intended to limit the scope, applicability,or configuration of the disclosure in any way. Rather, the foregoingdetailed description will provide those skilled in the art with aconvenient road map for implementing an exemplary embodiment of thedisclosure. It being understood that various changes may be made in thefunction and arrangement of elements described in an exemplaryembodiment without departing from the scope of the disclosure as setforth in the appended claims.

1. A method for isomerization of paraffins, the method comprising thesteps of: compressing a C₄ ⁻ hydrocarbons-containing stabilizer vaporstream from a stabilizer overhead receiver of a C₅/C₆ isomerizationsection to form a compressed C₄ ⁻ hydrocarbons-containing stabilizerstream; contacting in a C₄ isomerization section, a C₄hydrocarbons-containing feed stream that comprises unbranched C₄hydrocarbons with a chloride-promoted isomerization catalyst in thepresence of hydrogen to form a branched C₄ hydrocarbons-containingreaction zone effluent; combining at least a portion of the compressedC₄ ⁻ hydrocarbons-containing stabilizer stream with the branched C₄hydrocarbons-containing reaction zone effluent to form a C₄hydrocarbons-containing combined stream; and separating the C₄hydrocarbons-containing combined stream into a C₃⁻hydrocarbons-containing stabilizer vapor stream and a C₄hydrocarbons-rich product stream that comprises branched C₄hydrocarbons.
 2. The method of claim 1, wherein the step of compressingcomprises compressing the C₄ ⁻ hydrocarbons-containing stabilizer vaporstream to a pressure of from about 2760 to about 4210 kPa gauge to formthe compressed C₄ ⁻ hydrocarbons-containing stabilizer stream.
 3. Themethod of claim 1, wherein the step of combining comprises forming theC₄ hydrocarbons-containing combined stream having a pressure of fromabout 2000 to about 2760 kPa gauge.
 4. The method of claim 1, whereinthe step of combining comprises forming the C₄ hydrocarbons-containingcombined stream having a temperature of from about 30 to about 150° C.5. The method of claim 1, wherein the step of separating comprisesforming the C₃ ⁻ hydrocarbons-containing stabilizer vapor stream havinga pressure of from about 1000 to about 2410 kPa gauge.
 6. The method ofclaim 1, wherein the step of separating comprises forming the C₃ ⁻hydrocarbons-containing stabilizer vapor stream having a temperature offrom about −40 to about 45° C.
 7. The method of claim 1, furthercomprising the step of: demisting the C₄ ⁻ hydrocarbons-containingstabilizer vapor stream to remove mist droplets and/or deposits from theC₄ ⁻ hydrocarbons-containing stabilizer vapor stream prior to the stepof compressing.
 8. A method for isomerization of paraffins, the methodcomprising the steps of: Contacting, C₅/C₆ isoemrization section, a C₅ ⁺hydrocarbons-containing feed stream that comprises unbranched C₅/C₆hydrocarbons with a chloride-promoted isomerization catalyst in thepresence of hydrogen to form a branched C₅ ⁺ hydrocarbons-containingreaction zone effluent; separating the branched C₅ ⁺hydrocarbons-containing reaction zone effluent into a C₄ ⁻hydrocarbons-containing stabilizer vapor stream from a stabilizeroverhead receiver and a C₅ ⁺ hydrocarbon-rich product stream thatcomprises branched C₅ ⁺ hydrocarbons; compressing the C₄ ⁻hydrocarbons-containing stabilizer vapor stream to form a compressed C₄⁻ hydrocarbons-containing stabilizer stream; cooling the compressed C₄ ⁻hydrocarbons-containing stabilizer stream to form a cooled, compressedC₄ ⁻ hydrocarbons-containing stabilizer stream; and separating thecooled, compressed C₄ ⁻ hydrocarbons-containing stabilizer stream into aC₄ hydrocarbons-containing liquid stream and a C₃ ⁻hydrocarbons-containing off gas stream; combining the C₄hydrocarbons-containing liquid stream with a branched C₄hydrocarbons-containing reaction zone effluent from a C₄ isomerizationsection to form a C₄ hydrocarbons-containing combined stream; andseparating the C₄ hydrocarbons-containing combined stream into a C₃ ⁻hydrocarbons-containing stabilizer vapor stream and a C₄hydrocarbons-rich product stream that comprises branched C₄hydrocarbons.
 9. The method of claim 8, wherein the step of contactingcomprises contacting the chloride-promoted isomerization catalyst withthe C₅ ⁺ hydrocarbons-containing feed stream that further comprisescyclic C₆ ⁺ and C₇ ⁺ hydrocarbons.
 10. The method of claim 9, whereinthe step of contacting comprises contacting the chloride-promotedisomerization catalyst with the C₅ ⁺ hydrocarbons-containing feed streamthat comprises the cyclic C₆ ⁺ hydrocarbons and C₇ ⁺ hydrocarbons in anamount of about 10 wt. % or greater of the C₅ ⁺ hydrocarbons-containingfeed stream.
 11. The method of claim 8, wherein compressing comprisescompressing the C₄ ⁻ hydrocarbons-containing stabilizer vapor stream toa pressure of from about 2760 to about 4210 kPa gauge to form thecompressed C₄ ⁻ hydrocarbons-containing stabilizer stream.
 12. Themethod of claim 8, wherein compressing comprises forming the compressedC₄ ⁻ hydrocarbons-containing stabilizer stream having a temperature offrom about 70 to about 120° C.
 13. The method of claim 8, wherein thestep of cooling comprises forming the cooled, compressed C⁴ ⁻hydrocarbons-containing stabilizer stream having a temperature of fromabout 0 to about 45° C.
 14. The method of claim 8, wherein the step ofseparating the cooled, compressed C₄ ⁻ hydrocarbons-containingstabilizer stream comprises separating the cooled, compressed C₄ ⁻hydrocarbons-containing stabilizer stream at a pressure of from about2660 to about 4140 kPa gauge.
 15. The method of claim 8, wherein thestep of separating the cooled, compressed C₄ ⁻ hydrocarbons-containingstabilizer stream comprises separating the cooled, compressed C₄ ⁻hydrocarbons-containing stabilizer stream at a temperature of from about0 to about 45° C.
 16. The method of claim 8, further comprising thesteps of: combining at least a portion of the C₃ ⁻hydrocarbons-containing off gas stream with the C₃ ⁻hydrocarbons-containing stabilizer vapor stream to form a C₃ ⁻hydrocarbons-containing combined stream that comprises C₃ ⁻hydrocarbons, hydrogen, and HCl; and scrubbing the C₃ ⁻hydrocarbons-containing combined stream with a caustic to neutralizeHCl.
 17. The method of claim 8, further comprising the steps of:recycling at least a portion of the C₃ ⁻ hydrocarbons-containing off gasstream that comprises C₃ ⁻ hydrocarbons, hydrogen, and HCl back to theC₅ ⁺ hydrocarbons-containing feed stream.
 18. The method of claim 17,wherein the step of recycling comprises introducing that at least theportion of the C₃ ⁻ hydrocarbons-containing off gas stream to the C₅ ⁺hydrocarbons-containing feed stream at from about 30 to about 70% of amass flow rate of the C₃ ⁻ hydrocarbons-containing off gas stream. 19.The method of claim 8, further comprising the steps of: combining a C₄hydrocarbons-containing feed stream that comprises unbranched C₄hydrocarbons with at least a portion of the C₃ ⁻ hydrocarbons-containingoff gas stream that comprises C₃ ⁻ hydrocarbons, hydrogen, and HCl toform a combined stream; and contacting the combined stream with anisomerization catalyst to form the branched C₄ hydrocarbons-containingreaction zone effluent.
 20. (canceled)